The present invention relates to a hydrogenation catalyst. More particularly, the present invention relates to a catalyst suitable for use in a process by which a monocyclic aromatic hydrocarbon is partially reduced to produce a corresponding cycloolefin, in particular, cyclohexene in high selectivity and yield.
Cycloolefins are produced by partial hydrogenation, which is one kind of hydrogenation reaction, of aromatic hydrocarbon compounds. As is well known, it is difficult to obtain cycloolefins in high yield because the resulting cycloolefins are normally more reactive than the starting aromatic hydrocarbon compounds. If cycloolefins can be obtained in high yield by partial hydrogenation of aromatic hydrocarbon compounds, the reaction process can be simplified, which is preferred from an industrial viewpoint.
Various hydrogenation catalysts are employed in the process for producing cycloolefins by partial hydrogenation of aromatic hydrocarbon compounds, and the followings are typical examples:
(1) a catalyst composition containing water, an alkali agent and an element of group VIII in the periodic table (Japanese Patent Publication No. 56-22850); PA0 (2) a ruthenium catalyst containing copper, silver, cobalt or potassium which is to be used together with water and a phosphate compound (Japanese Patent Publication No. 56-4536); PA0 (3) a catalyst having chiefly ruthenium supported on a metal oxide such as silica or alumina and which is to be used in a process of performing partial hydrogenation in the presence of water and cobalt sulfate (Japanese Patent Public Disclosure No. 57-130926); PA0 (4) a ruthenium catalyst supported on an oxide of nickel, cobalt, chromium, titanium or zirconium which is to be used in a process employing an alcohol or ester as an additive (Japanese Patent Publication No. 52-3933); PA0 (5) a ruthenium-silica catalyst for use in a process of performing partial hydrogenation in the presence of water which is prepared by hydrolyzing a mixed solution of ruthenium glycoxide and ethyl silicate, then reducing the hydrolyzate with hydrogen at 400.degree. C. (Japanese Patent Public Disclosure No. 59-155328); PA0 (6) a ruthenium catalyst for use in a process of performing reaction with at least one of zinc oxide and zinc hydroxide being added as an activating component to the reaction system (Japanese Patent Public Disclosure No. 59-184138); PA0 (7) a catalyst prepared by reducing Zn-containing ruthenium which is to be used in a process of performing partial hydrogenation in the presence of a water-soluble zinc compound (Japanese Patent Public Disclosure No. 62-45544); and PA0 (8) a catalyst having a ruthenium-based mixture of metallic elements supported on barium sulfate which is to be used in a process of performing reaction in the presence of one compound selected from among silicon dioxide, titanium dioxide and aluminum oxide (Japanese Patent Public Disclosure No. 62-61935).
However, if hydrogenation is performed using the known catalysts listed above, the conversion of the starting material must be held low in order to enhance the selectivity for the desired cyclohexenes, or the reaction rate is very low. Because of these and other reasons, the yield and production rate of cyclohexenes are generally low in the conventional processes. Furthermore, these processes are not necessarily best suited for commercial production of cyclohexenes because the use of large amounts of additives causes various problems such as increased complexity of the reaction system and the need to employ a corrosion-resistant reactor.
Under these circumstances, there has been a strong need for the development of a hydrogenation catalyst that allows the intended product to be obtained in high selectivity and yield.